The invention is directed to improvements in fuel injection pumps provided with dual work chambers.
In a fuel injection pump of this kind, disclosed in German Offenlegungsschrift DE-OS 31 17 220, each pump work chamber communicates continuously with a respective relief line; these relief lines extend in the pump piston and have separate outlets on the pump piston and are controlled there by the slide. Also leading from each relief line is a respective transverse connection to each of the distributor openings, which cooperate with supply lines correspondingly distributed on the circumference of the stepped bore. In the known fuel injection pump, every pump work chamber is supplied with filling grooves, in the form of longitudinal grooves, during the intake stroke of the pump piston. Furthermore, the first pump work chamber communicates continuously with the relief chamber from the onset of the pump piston stroke until a predetermined stroke position.
This fuel injection pump operates in such a way that the fuel that is positively displaced out of the second pump work chamber continuously communicates with the fuel injection line, that is, from the onset of the pump piston supply stroke forward. Also, in addition to the fuel injection quantity that is positively displaced from the second pump work chamber, the fuel that is positively displaced, at high pressure, from the first work chamber also comes to be injected beyond a predetermined pump piston stroke.
This known apparatus has the disadvantage that it not only is very complicated in terms of distributing the fuel from the second pump work chamber and the first work chamber, but it also has very long injection times in full-load operation, which is very disadvantageous, especially if the fuel injection pump is intended for supplying an internal combustion engine that operates with direct injection. In particular, the injection duration in the known pump is shorter in the idling range than in the full-load range, which has an unfavorable effect both in terms of noise and in terms of engine performance. It is also unfavorable that the injection rate increases suddenly at the instant that the supply from the first pump work chamber is added. At this point of non-steady engine operation, governing problems must be expected.